Forbes, August 28, 2007
William McGrew spent much of the 1970s observing chimpanzees in Tanzania. One day the chimps did something odd. As two chimpanzees groomed each other’s hair, they each lifted an arm overhead. They clasped hands, forming a kind of primate A-frame.
McGrew and his collaborator, Caroline Tutin, had just spent months observing another chimpanzee community just a hundred miles away, and they had never seen that gesture before. But at their new field site, the A-frame handshake turned out to be common.